Clamped monolithic showerhead electrode

ABSTRACT

An electrode assembly for a plasma reaction chamber used in semiconductor substrate processing. The assembly includes an upper showerhead electrode which is mechanically attached to a backing plate by a series of spaced apart cam locks. A guard ring surrounds the backing plate and is movable to positions at which openings in the guard ring align with openings in the backing plate so that the cam locks can be rotated with a tool to release locking pins extending from the upper face of the electrode.

FIELD OF THE INVENTION

The invention relates to a showerhead electrode assembly of a plasmaprocessing chamber in which semiconductor components can bemanufactured.

SUMMARY

According to one embodiment, a showerhead electrode assembly comprises amonolithic stepped electrode clamped to a backing plate wherein theshowerhead electrode assembly comprises an upper electrode of acapacitively coupled plasma processing chamber. The stepped electrode isa circular plate having a plasma exposed surface on a lower face thereofand a mounting surface on an upper face thereof. The mounting surfaceincludes a plurality of alignment pin recesses configured to receivealignment pins arranged in a pattern matching alignment pin holes in abacking plate against which the plate is held by cam locks and the plateincludes process gas outlets arranged in a pattern matching gas supplyholes in the backing plate. The upper face includes an outer recessedsurface surrounding a planar inner surface, the plasma exposed surfaceincluding inner and outer inclined surfaces. A plurality ofcircumferentially spaced apart pockets in the outer recessed surface areconfigured to receive locking pins therein adapted to cooperate with camlocks to clamp the stepped electrode to the backing plate.

According to another embodiment, a showerhead electrode assembly of acapacitively coupled plasma processing chamber comprises a thermalcontrol plate, a backing plate, a guard ring and a stepped electrode.The thermal control plate is supported by a temperature controlled wallof the plasma processing chamber, the thermal control plate having adiameter larger than a wafer to be processed in the plasma processingchamber and including annular projections on a lower side thereof withgas plenums between the annular projections. The backing plate issupported by the thermal control plate and has a diameter smaller thanthe thermal control plate, gas passages therethrough, and cam locks inhorizontally extending bores. The shield ring has a height equal to athickness of the outer periphery of the backing plate and at least onehorizontally extending access bore passing through the shield ring, theshield ring being rotatable around the backing plate to align the accessbore with at least one of the cam locks. The stepped electrode has gaspassages therethrough in fluid communication with the gas passages inthe backing plate The stepped electrode includes vertically extendinglocking pins which engage the cam locks, the stepped electrodesupporting the shield ring and being removable by releasing the lockingpins from the cam locks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a showerhead electrode assemblyforming an upper electrode of a capacitively coupled plasma reactor foretching substrates having a guard ring.

FIG. 2A is a three-dimensional representation of an exemplary cam lockfor clamping a stepped electrode in the reactor shown in FIG. 1.

FIG. 2B is a cross-sectional view of the exemplary cam lock electrodeclamp of FIG. 2A.

FIG. 3 shows side-elevation and assembly drawings of an exemplarylocking pin used in the cam lock clamp of FIGS. 2A and 2B.

FIG. 4A shows side-elevation and assembly drawings of an exemplary camshaft used in the cam lock clamp of FIGS. 2A and 2B.

FIG. 4B shows a cross-sectional view of an exemplary cutter-path edge ofa portion of the cam shaft of FIG. 4A.

FIG. 5 shows a showerhead electrode assembly with a stepped electrode,backing plate, thermal control plate, guard ring and top plate.

FIGS. 6A and 6B are perspective views of the stepped electrode.

FIG. 7 is a perspective view of a backing plate.

FIG. 8 is a perspective view of the showerhead electrode assemblywithout the guard ring.

DETAILED DESCRIPTION

The fabrication of an integrated circuit chip typically begins with athin, polished slice of high-purity, single-crystal semiconductormaterial substrate (such as silicon or germanium) called a “wafer.” Eachwafer is subjected to a sequence of physical and chemical processingsteps that form the various circuit structures on the wafer. During thefabrication process, various types of thin films may be deposited on thewafer using various techniques such as thermal oxidation to producesilicon dioxide films, chemical vapor deposition to produce silicon,silicon dioxide, and silicon nitride films, and sputtering or othertechniques to produce other metal films.

After depositing a film on the semiconductor wafer, the uniqueelectrical properties of semiconductors are produced by substitutingselected impurities into the semiconductor crystal lattice using aprocess called doping. The doped silicon wafer may then be uniformlycoated with a thin layer of photosensitive, or radiation sensitivematerial, called a “resist.” Small geometric patterns defining theelectron paths in the circuit may then be transferred onto the resistusing a process known as lithography. During the lithographic process,the integrated circuit pattern may be drawn on a glass plate called a“mask” and then optically reduced, projected, and transferred onto thephotosensitive coating.

The lithographed resist pattern is then transferred onto the underlyingcrystalline surface of the semiconductor material through a processknown as etching. Vacuum processing chambers are generally used foretching and chemical vapor deposition (CVD) of materials on substratesby supplying an etching or deposition gas to the vacuum chamber andapplication of a radio frequency (RF) field to the gas to energize thegas into a plasma state.

A reactive ion etching system typically consists of an etching chamberwith an upper electrode or anode and a lower electrode or cathodepositioned therein. The cathode is negatively biased with respect to theanode and the container walls. The wafer to be etched is covered by asuitable mask and placed directly on the cathode. A chemically reactivegas such as CF₄, CHF₃, CClF₃, HBr, Cl₂ and SF₆ or mixtures thereof withO₂, N₂, He or Ar is introduced into the etching chamber and maintainedat a pressure which is typically in the millitorr range. The upperelectrode is provided with gas hole(s), which permit the gas to beuniformly dispersed through the electrode into the chamber. The electricfield established between the anode and the cathode will dissociate thereactive gas forming plasma. The surface of the wafer is etched bychemical interaction with the active ions and by momentum transfer ofthe ions striking the surface of the wafer. The electric field createdby the electrodes will attract the ions to the cathode, causing the ionsto strike the surface in a predominantly vertical direction so that theprocess produces well-defined vertically etched sidewalls. The etchingreactor electrodes may often be fabricated by bonding two or moredissimilar members with mechanically compliant and/or thermallyconductive adhesives, allowing for a multiplicity of function.

FIG. 1 shows a cross-sectional view of a portion of a showerheadelectrode assembly 100 of a plasma processing system for etchingsubstrates. As shown in FIG. 1, the showerhead electrode assembly 100includes a stepped electrode 110, a backing plate 140, and a guard ring(or outer ring) 170. The showerhead electrode assembly 100 also includesa plasma confinement assembly (or wafer area pressure (WAP) assembly)180, which surrounds the outer periphery of the upper electrode 110 andthe backing plate 140.

The assembly 100 also includes a thermal control plate 102, and an upper(top) plate 104 having liquid flow channels therein and forming atemperature controlled wall of the chamber. The stepped electrode 110 ispreferably a cylindrical plate and may be made of a conductive highpurity material such as single crystal silicon, polycrystalline silicon,silicon carbide or other suitable material (such as aluminum or alloythereof, anodized aluminum, yttria coated aluminum). The backing plate140 is mechanically secured to the electrode 110 with mechanicalfasteners described below. The guard ring 170 surrounds the backingplate 140 and provides access to cam locking members as described below.

The showerhead electrode assembly 100 as shown in FIG. 1 is typicallyused with an electrostatic chuck (not shown) incorporating a flat lowerelectrode on which a wafer is supported at a distance of about 1 to 2 cmbelow the upper electrode 110. An example of such a plasma processingsystem is a parallel plate type reactor, such as the Exelan® dielectricetch systems, made by Lam Research Corporation of Fremont, Calif. Suchchucking arrangements provide temperature control of the wafer bysupplying backside helium (He) pressure, which controls the rate of heattransfer between the wafer and the chuck. In embodiments, during plasmaprocessing, the upper showerhead electrode is grounded and the bottom(lower) electrode is powered.

The upper electrode 110 is a consumable part which must be replacedperiodically. To supply process gas to the gap between the wafer and theupper electrode, the upper electrode 110 is provided with a gasdischarge passages 106, which are of a size and distribution suitablefor supplying a process gas, which is energized by the electrode andforms plasma in a reaction zone beneath the upper electrode 110.

The showerhead electrode assembly 100 also includes a plasma confinementassembly (or wafer area plasma (WAP) assembly) 180, which surrounds theouter periphery of the upper electrode 110 and the backing plate 140.The plasma confinement assembly 180 is preferably comprised of a stackor plurality of spaced-apart quartz rings 190, which surrounds the outerperiphery of upper electrode 110 and the backing plate 140. Duringprocessing, the plasma confinement assembly 180 causes a pressuredifferential in the reaction zone and increases the electricalresistance between the reaction chamber walls and the plasma therebyconfining the plasma between the upper electrode 110 and the lowerelectrode (not shown).

During use, the confinement rings 190 confine the plasma to the chambervolume and controls the pressure of the plasma within the reactionchamber. The confinement of the plasma to the reaction chamber is afunction of many factors including the spacing between the confinementrings 190, the pressure in the reaction chamber outside of theconfinement rings and in the plasma, the type and flow rate of the gas,as well as the level and frequency of RF power. Confinement of theplasma is more easily accomplished if the spacing between theconfinement rings 190 is very small. Typically, a spacing of 0.15 inchesor less is required for confinement. However, the spacing of theconfinement rings 190 also determines the pressure of the plasma, and itis desirable that the spacing can be adjusted to achieve the pressurerequired for optimal process performance while maintaining plasma.Process gas from a gas supply is supplied to electrode 110 through oneor more passages in the upper plate 104 which permit process gas to besupplied to a single zone or multiple zones above the wafer.

The electrode 110 is preferably a planar disk or plate having a uniformthickness from center (not shown) to an area of increased thicknessforming a step on the plasma exposed surface extending inwardly from anouter edge. The electrode 110 preferably has a diameter larger than awafer to be processed, e.g., over 300 mm. The diameter of the upperelectrode 110 can be from about 15 inches to about 17 inches forprocessing 300 mm wafers. The upper electrode 110 preferably includesmultiple gas passages 106 for injecting a process gas into a space in aplasma reaction chamber below the upper electrode 110.

Single crystal silicon and polycrystalline silicon are preferredmaterials for plasma exposed surfaces of the electrode 110. High-purity,single crystal or polycrystalline silicon minimizes contamination ofsubstrates during plasma processing as it introduces only a minimalamount of undesirable elements into the reaction chamber, and also wearssmoothly during plasma processing, thereby minimizing particles.Alternative materials including composites of materials that can be usedfor plasma-exposed surfaces of the upper electrode 110 include aluminum(as used herein “aluminum” refers to pure Al and alloys thereof), yttriacoated aluminum, SiC, SiN, and AlN, for example.

The backing plate 140 is preferably made of a material that ischemically compatible with process gases used for processingsemiconductor substrates in the plasma processing chamber, has acoefficient of thermal expansion closely matching that of the electrodematerial, and/or is electrically and thermally conductive. Preferredmaterials that can be used to make the backing plate 140 include, butare not limited to, graphite, SiC, aluminum (Al), or other suitablematerials.

The upper electrode 110 is attached mechanically to the backing plate140 without any adhesive bonding between the electrode and backingplate, i.e., a thermally and electrically conductive elastomeric bondingmaterial is not used to attach the electrode to the backing plate.

The backing plate 140 is preferably attached to the thermal controlplate 102 with suitable mechanical fasteners, which can be threadedbolts, screws, or the like. For example, bolts (not shown) can beinserted in holes in the thermal control plate 102 and screwed intothreaded openings in the backing plate 140. The thermal control plate102 includes a flexure portion 184 and is preferably made of a machinedmetallic material, such as aluminum, an aluminum alloy or the like. Theupper temperature controlled plate 104 is preferably made of aluminum oran aluminum alloy. The plasma confinement assembly (or wafer area plasmaassembly (WAP)) 180 is positioned outwardly of the showerhead electrodeassembly 100. A suitable plasma confinement assembly 180 including aplurality of vertically adjustable plasma confinement rings 190 isdescribed in commonly owned U.S. Pat. No. 5,534,751, which isincorporated herein by reference in its entirety.

The upper electrode can be mechanically attached to the backing plate bya cam lock mechanism as described in commonly-owned U.S. applicationSer. No. 61/036,862, filed Mar. 14, 2008, the disclosure of which ishereby incorporated by reference. With reference to FIG. 2A, athree-dimensional view of an exemplary cam lock electrode clamp includesportions of an electrode 201 and a backing plate 203. The electrodeclamp is capable of quickly, cleanly, and accurately attaching aconsumable electrode 201 to a backing plate in a variety of fab-relatedtools, such as the plasma etch chamber shown in FIG. 1.

The electrode clamp includes a stud (locking pin) 205 mounted into asocket 213. The stud may be surrounded by a disc spring stack 215, such,for example, stainless steel Belleville washers. The stud 205 and discspring stack 215 may then be press-fit or otherwise fastened into thesocket 213 through the use of adhesives or mechanical fasteners. Thestud 205 and the disc spring stack 215 are arranged into the socket 213such that a limited amount of lateral movement is possible between theelectrode 201 and the backing plate 203. Limiting the amount of lateralmovement allows for a tight fit between the electrode 201 and thebacking plate 203, thus ensuring good thermal contact, while stillproviding some movement to account for differences in thermal expansionbetween the two parts. Additional details on the limited lateralmovement feature are discussed in more detail, below.

In a specific exemplary embodiment, the socket 213 is fabricated frombearing-grade Torlon®. Alternatively, the socket 213 may be fabricatedfrom other materials possessing certain mechanical characteristics suchas good strength and impact resistance, creep resistance, dimensionalstability, radiation resistance, and chemical resistance may be readilyemployed. Various materials such as polyamides, polyimides, acetals, andultra-high molecular weight polyethylene materials may all be suitable.High temperature-specific plastics and other related materials are notrequired for forming the socket 213 as 230° C. is a typical maximumtemperature encountered in applications such as etch chambers.Generally, a typical operating temperature is closer to 130° C.

Other portions of the electrode clamp are comprised of a camshaft 207surrounded at each end by a pair of camshaft bearings 209. The camshaft207 and camshaft bearing assembly is mounted into a backing plate bore211 machined into the backing plate 203. In a typical application for anetch chamber designed for 300 mm semiconductor wafers, eight or more ofthe electrode clamps may be spaced around the periphery of the electrode201/backing plate 203 combination.

The camshaft bearings 209 may be machined from a variety of materialsincluding Torlon®, Vespel®, Celcon®, Delrin®, Teflon®, Arlon®, or othermaterials such as fluoropolymers, acetals, polyamides, polyimides,polytetrafluoroethylenes, and polyetheretherketones (PEEK) having a lowcoefficient of friction and low particle shedding. The stud 205 andcamshaft 207 may be machined from stainless steel (e.g., 316, 316L,17-7, etc.) or any other material providing good strength and corrosionresistance.

Referring now to FIG. 2B, a cross-sectional view of the electrode camclamp further exemplifies how the cam clamp operates by pulling theelectrode 201 in close proximity to the backing plate 203. The stud205/disc spring stack 215/socket 213 assembly is mounted into theelectrode 201. As shown, the assembly may be screwed, by means ofexternal threads on the socket 213 into a threaded pocket in theelectrode 201. However, the socket may be mounted by adhesives or othertypes of mechanical fasteners as well.

In FIG. 3, an elevation and assembly view 300 of the stud 205 having anenlarged head, disc spring stack 215, and socket 213 provides additionaldetail into an exemplary design of the cam lock electrode clamp. In aspecific exemplary embodiment, a stud/disc spring assembly 301 is pressfit into the socket 213. The socket 213 has an external thread and ahexagonal top member allowing for easy insertion into the electrode 201(see FIGS. 2A and 2B) with light torque (e.g., in a specific exemplaryembodiment, about 20 inch-pounds). As indicated above, the socket 213may be machined from various types of plastics. Using plastics minimizesparticle generation and allows for a gall-free installation of thesocket 213 into a mating pocket on the electrode 201.

The stud/socket assembly 303 illustrates an inside diameter in an upperportion of the socket 213 being larger than an outside diameter of amid-section portion of the stud 205. The difference in diameters betweenthe two portions allows for the limited lateral movement in theassembled electrode clamp as discussed above. The stud/disc springassembly 301 is maintained in rigid contact with the socket 213 at abase portion of the socket 213 while the difference in diameters allowsfor some lateral movement. (See also, FIG. 2B.)

With reference to FIG. 4A, an exploded view 400 of the camshaft 207 andcamshaft bearings 209 also indicates a keying pin 401. The end of thecamshaft 207 having the keying pin 401 is first inserted into thebacking plate bore 211 (see FIG. 2B). A pair of small mating holes (notshown) at a far end of the backing plate bore 211 provide properalignment of the camshaft 207 into the backing plate bore 211. Aside-elevation view 420 of the camshaft 207 clearly indicates a possibleplacement of a hex opening 403 on one end of the camshaft 207 and thekeying pin 401 on the opposite end.

For example, with continued reference to FIGS. 4A and 2B, the electrodecam clamp is assembled by inserting the camshaft 207 into the backingplate bore 211. The keying pin 401 limits rotational travel of thecamshaft 207 in the backing plate bore 211 by interfacing with one ofthe pair of small mating holes. The camshaft may first be turned in onedirection though use of the hex opening 403, for example,counterclockwise, to allow entry of the stud 205 into the camshaft 207,and then turned clockwise to fully engage and lock the stud 205. Theclamp force required to hold the electrode 201 to the backing plate 203is supplied by compressing the disc spring stack 215 beyond their freestack height. The camshaft 207 has an internal eccentric internal cutoutwhich engages the enlarged head of the shaft 205. As the disc springstack 215 compresses, the clamp force is transmitted from individualsprings in the disc spring stack 215 to the socket 213 and through theelectrode 201 to the backing plate 203.

In an exemplary mode of operation, once the camshaft bearings areattached to the camshaft 207 and inserted into the backing plate bore211, the camshaft 207 is rotated counterclockwise to its full rotationaltravel. The stud/socket assembly 303 (FIG. 3) is then lightly torquedinto the electrode 201. The head of the stud 205 is then inserted intothe vertically extending through hole below the horizontally extendingbacking plate bore 211. The electrode 201 is held against the backingplate 203 and the camshaft 207 is rotated clockwise until either thekeying pin drops into the second of the two small mating holes (notshown) or an audible click is heard (discussed in detail, below). Theexemplary mode of operation may be reversed to dismount the electrode201 from the backing plate 203. However, features such as the audibleclick are optional in the cam lock arrangement.

With reference to FIG. 4B, a sectional view A-A of the side-elevationview 420 of the camshaft 207 of FIG. 4A indicates a cutter path edge 440by which the head of the stud 205 is fully secured. In a specificexemplary embodiment, the two radii R₁ and R₂ are chosen such that thehead of the stud 205 makes the optional audible clicking noise describedabove to indicate when the stud 205 is fully secured.

FIG. 5 illustrates an upper electrode assembly 500 for a capacitivelycoupled plasma chamber which includes the following features: (a) acam-locked non-bonded electrode 502; (b) a backing plate 506; and (c) aguard ring 508 which allows access to cam locks holding the electrode tothe backing plate 506.

The electrode assembly 500 includes a thermal control plate 510 boltedfrom outside the chamber to a temperature controlled top wall 512 of thechamber. The electrode 502 is releasably attached to the backing platefrom inside the chamber by cam-lock mechanisms 514 described earlierwith reference to FIGS. 2-4.

In a preferred embodiment, the electrode 502 of the electrode assembly500 can be disassembled by (a) rotating the guard ring 508 to a firstposition aligning four holes in the guard ring with four cam locks 514located at spaced positions in the outer portion of the backing plate;(b) inserting a tool such as an alien wrench through each hole in theguard ring and rotating each cam lock to release a vertically extendinglocking pin of each respective cam lock; (c) rotating the guard ring 90°to a second position aligning the four holes in the guard ring withanother four cam locks; and (d) inserting a tool such as an allen wrenchthrough each hole in the guard ring and rotating each respective camlock to release a locking pin of each respective cam lock; whereby theelectrode 502 can be lowered and removed from the plasma chamber.

FIG. 5 also shows a cross-sectional view of one of the cam lockarrangements wherein a rotatable cam lock 514 is located in ahorizontally extending bore 560 in an outer portion of the backing plate506. The cylindrical cam lock 514 is rotatable by a tool such as anallen wrench to (a) a lock position at which an enlarged end of alocking pin 562 is engaged by a cam surface of the cam lock 514 whichlifts the enlarged head of the locking pin or (b) a release position atwhich the locking pin 562 is not engaged by the cam lock 514. Thebacking plate includes vertically extending bores in its lower facethrough which the locking pins are inserted to engage the cam locks.

FIGS. 6A-B show details of the electrode 502. The electrode 502 ispreferably a plate of high purity (less than 10 ppm impurities) lowresistivity (0.005 to 0.02 ohm-cm) single crystal silicon with alignmentpin holes 520 in an upper face (mounting surface) 522 which receivealignment pins 524. Gas holes 528 extend from the upper face to thelower face (plasma exposed surface) 530 and can be arranged in anysuitable pattern. In the embodiment shown, the gas holes are arranged in13 circumferentially extending rows with three gas holes in the firstrow located about 0.5 inch from the center of the electrode, 13 gasholes in the second row located about 1.4 inches from the center, 23 gasholes in the third row located about 2.5 inches from the center, 25 gasholes in the fourth row located about 3.9 inches from the center, 29 gasholes in the fifth row located about 4.6 inches from the center, 34 gasholes in the sixth row located about 5.4 inches from the center, 39 gasholes in the seventh row located about 6 inches from the center, 50 gasholes in the eighth row located about 7.5 inches from the center, 52 gasholes in the ninth row located about 8.2 inches from the center, 53 gasholes in the tenth row located about 9 inches from the center, 57 gasholes in the eleventh row located about 10.3 inches from the center, 59gas holes in the twelfth row located about 10.9 inches from the centerand 63 holes in the thirteenth row located about 11.4 inches from thecenter.

The upper face of the electrode includes 9 alignment pin holes with 3pin holes near the center, 3 pin holes inward of the annular recess and3 pin holes in the annular recess near the outer edge of the electrode.The 3 central pin holes are radially aligned and include a pin hole atthe center of the inner electrode and 2 pin holes between the third andfourth rows of gas holes. The intermediate pin holes near the annularrecess include one pin hole radially aligned with the central pin holeand two other pin holes spaced 120° apart. The outer 3 pin holes arespaced 120° apart at locations between adjacent pockets.

FIG. 6A is a front perspective view showing the plasma exposed surface530 of the electrode 502 with the 13 rows of gas holes. FIG. 6B shows aperspective view of the upper face with the 13 rows of gas holes. Theelectrode 502 includes a confined pattern of holes 529 in the steppedouter surface 546 to cooperate with a manometer unit to provide vacuumpressure measurements in the chamber.

The electrode 502 includes an outer step (ledge) 536 which supports theguard ring 508, the upper face (mounting surface) 522 which engages alower surface of the backing plate 506, the lower face (plasma exposedstepped surface) 530 which includes inner tapered surface 544, ahorizontal surface 546, and an outer tapered surface 548 and 8 pockets550 in upper face 540 in which the locking pins are mounted.

FIG. 7 is a perspective view of backing plate 506. The backing plate isfree of thermal control coolant passages and heating elements. Thebacking plate includes 13 rows of gas passages 584 which align with thepassages 528 in the showerhead electrode 502. The upper face 586 of thebacking plate includes three annular regions 588 a, 588 b, 588 c whichcontact annular projections of the thermal control plate 510. Thethermal control plate can be attached to the top wall of the plasmachamber by fasteners extending through the top wall into the thermalcontrol plate as disclosed in commonly-assigned U.S. Patent PublicationNos. 2005/0133160, 2007/0068629, 2007/0187038, 2008/0087641 and2008/0090417, the disclosures of which are hereby incorporated in theirentirety. Threaded openings 590 are located in an outer periphery of theupper face 586 and the annular regions 588 a, 588 b, 588 c to receivefasteners extending through openings in the top plate 512 and thermalcontrol plate 510 to hold the backing plate 506 in contract with thethermal control plate 510. See, for example, commonly-assigned U.S.Patent Publication No. 2008/0087641 for a description of fasteners whichcan accommodate thermal cycling. A groove 592 in the upper face 586receives an O-ring which provides a gas seal between the backing plate506 and the thermal control plate 510. The gas seal is located outwardlyof the gas passages in the backing plate. Alignment pin bores 594 in theupper face 586 receive alignment pins which fit into alignment pin boresin the thermal control plate. Horizontally extending threaded openings561 at positions between bores 560 receive dielectric fasteners used toprevent the guard ring from rotating and plug the access bores in theguard ring after assembly of the showerhead electrode.

FIG. 8 is a perspective view of the showerhead electrode assembly 500with the guard ring removed. As explained earlier, the guard ring can berotated to one or more assembly positions at which the cam locks can beengaged and rotated to a lock position at which dielectric fasteners canbe inserted into openings 561 to maintain the guard ring out of contactwith the outer periphery of the backing plate and thus allow for thermalexpansion of the backing plate. The thermal control plate includes aflange 595 with openings 596 through which actuators support the plasmaconfinement rings. Details of the mounting arrangement of plasmaconfinement ring assemblies can be found in commonly-assigned U.S.Patent Publication No. 2006/0207502 and 2006/0283552, the disclosures ofwhich are hereby incorporated in their entirety.

The mounting surface 522 of the electrode abuts an opposed surface ofthe backing plate 506 as a result of the clamping force exerted by the 8locking pins held by the 8 cam locks in the backing plate. The guardring 508 covers the mounting holes in the backing plate 506 and theaccess openings in the guard ring are filled with removable inserts madeof plasma resistant polymer material such as Torlon®, Vespel®, Celcon®,Delrin®, Teflon®, Arlon®, or other materials such as fluoropolymers,acetals, polyamides, polyimides, polytetrafluoroethylenes, andpolyetheretherketones (PEEK) having a low coefficient of friction andlow particle shedding.

With reference to FIG. 5, electrical contact between the backing plate506 and electrode 502 is provided by one or more Q-pads 556 located atthe outer periphery of the electrode and at one or more locationsbetween the central alignment pin and the outer Q-pad. For example,Q-pads having diameters of about 4 and 12 inches can be used.Commonly-owned U.S. application Ser. No. 11/896,375, filed Aug. 31,2007, includes details of Q-pads, the disclosure of which is herebyincorporated by reference. To provide different process gas mixturesand/or flow rates, one or more optional gas partition seals can beprovided between the center alignment pin and the outer Q-pad. Forexample, a single O-ring can be provided between the electrode 502 andthe backing plate 506 at a location between the inner and outer Q-padsto separate an inner gas distribution zone from an outer gasdistribution zone. An O-ring 558 located between the electrode 502 andthe backing plate 506 along the inner periphery of the outer Q-pad canprovide a gas and particle seal between the electrode and backing plate.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A method of treating a semiconductor substrate ina plasma chamber, said method comprising the steps of: supporting thesemiconductor substrate on a bottom electrode in the chamber; supplyingprocess gas to the chamber; forming a plasma adjacent an exposed surfaceof an upper electrode, the upper electrode comprising a showerheadelectrode comprising: a central portion and a peripheral portion definedby upper and lower faces of the showerhead electrode, the upper faceincluding a planar surface extending across the central portion, thelower face defined by a planar inner surface extending across thecentral portion and a stepped outer surface extending across theperipheral portion, the stepped outer surface including an annularplanar surface defining an area of increased thickness of the showerheadelectrode; a plurality of gas outlets in the central portion of theelectrode through which process gas can be delivered to a gap betweenthe showerhead electrode and a lower electrode on which thesemiconductor substrate is supported; and a plurality ofcircumferentially spaced apart pockets in the upper face, the pocketsconfigured to receive cam locks therein adapted to clamp the showerheadelectrode to a backing plate; heating the showerhead electrode andbacking plate to an elevated temperature which causes differentialthermal expansion of the showerhead electrode and the backing plate, andaccommodating the thermal expansion by movement of locking pins; andprocessing the semiconductor substrate with the plasma.
 2. The method asclaimed in claim 1, wherein temperature of the showerhead electrode iscontrolled by a temperature controlled top wall of the chamber, athermal control plate and the backing plate, the thermal control plateincluding annular projections forming plenums between the thermalcontrol plate and the backing plate, wherein the plenums are in fluidcommunication with gas passages in the backing plate aligned with thegas passages in the showerhead electrode, and the backing plate providesa thermal path between the showerhead electrode and the thermal controlplate.
 3. The method as claimed in claim 1, wherein the semiconductorsubstrate comprises a semiconductor wafer and the processing stepcomprises etching the semiconductor wafer with the plasma.
 4. The methodas claimed in claim 1, wherein the upper electrode is grounded and thebottom electrode is powered during the processing step.
 5. The method ofclaim 1, wherein a confined pattern of gas holes in the stepped outersurface cooperates with a manometer unit to provide vacuum pressuremeasurements in the chamber.
 6. The method of claim 1, wherein theshowerhead electrode is a plate of polycrystalline silicon, singlecrystal silicon, silicon carbide, aluminum, anodized aluminum or yttriacoated aluminum.
 7. The method of claim 1, wherein the showerheadelectrode is attached to the backing plate and a thermal control plateis attached to the backing plate, the thermal control plate havingannular projections on a lower surface thereof defining gas plenums incommunication with the gas passages in the backing plate.
 8. The methodof claim 7, wherein the backing plate is free of thermal control coolantpassages and heating elements.
 9. The method of claim 7, wherein a gasseal is between the backing plate and the showerhead electrode, the gasseal being located outwardly of the gas passages.